In the medical field, and in other fields as well, there has developed a need for substrates with surfaces that become lubricious upon contact with water. A main use of lubricious materials involves catheters, catheter guide wires, and other medical devices that are meant to be inserted into the body. The lubricious nature of such materials allows the insertion (and subsequent removal) of a catheter or other medical device to be accomplished with minimum resistance, thereby reducing discomfort and possible injury.
In many cases, it is easy to prepare a functional lubricious coating for a substrate surface. However, it is more difficult to prepare a lubricious coating that is securely anchored to the substrate surface. Secure anchoring of a lubricious coating to a substrate surface is generally desirable, and particularly useful in the medical field, where secure anchorage of the coating is often an important requirement.
U.S. Pat. No. 4,642,267 to Creasy et al. discloses a hydrophilic polymer blend comprising a thermoplastic polyurethane and a poly(N-vinyl lactam). When used as a coating material, the polymer blend components are co-dissolved in an organic solvent capable of solubilizing both polymers, a substrate is dip coated in the solution, and the solvent is then driven off by a drying process so as to form a hydrophilic coating on the substrate surface. However, the coating attachment to the substrate is considered to lack the security desired. Another disadvantage of the '267 patent is that high boiling point and potentially toxic solvents are used to deliver the coating formulation, and thus significant costs must be incurred to drive off the solvent residuals from the coated product so as to obtain the desired biocompatibility.
U.S. Pat. No. 5,702,754 to Zhong discloses coating a substrate surface with a polymer having reactive functional groups and an excess of cross-linking agent. The polymer is cured to form a coating. Then, a second coating comprising a hydrophilic polymer having the same type of reactive functional groups is applied thereover. When the hydrophilic polymer is then cured, the second coating becomes covalently bonded to the first coating because the first coating includes an excess of cross-linking agent thereby permitting covalent bonding between the first coating and the hydrophilic polymer. Disadvantages of this approach include the fact that multiple steps are required and multiple polymer solutions are involved. There are also significant limitations in the selection of lubricious polymers and cross-linking agents.